The present invention relates to soil sampling devices and methods, and in particular to soil sampling devices that periodically and automatically take soil samples over an area of interest and store them for later analysis, and related methods.
In order to optimize the production capacity of any agricultural land, the grower must provide in each plot of soil the amount of fertilizers and other nutrients and additives that will render each plot ideal for the crop that is to be sewn and harvested. The grower cannot know how much fertilizer or other additives should be placed at a plot of soil, however, without knowing the current level of nutrients and important minerals that are already present in each plot. The quantity of these various materials present will vary greatly depending upon such factors as the soil type, the history of crops grown, and additives that have been previously applied to the field. It is thus a common practice for growers to periodically remove soil samples from various regions on their agricultural lands, which are then analyzed to determine the level of various important nutrients and minerals that they contain. It would also be highly desirable to know the level of compaction of soil in various regions, in order to properly gauge the steps necessary to arrive at the proper level of soil compaction for a particular crop to be grown in each region, although this testing is not commonly performed today.
Soil sampling has historically been a process performed by hand. Various hand tools have been developed to somewhat ease the burden of this task, but any manual operation to perform soil sampling is necessary tiresome and time-consuming because of the expanse of land that must be covered when soil sampling is performed as part of a large-scale commercial farming enterprise. Not only must a worker remove each sample, but the sample must then be transported back to a laboratory for analysis, and the samples must be transported in such a manner that samples from various plots are not mixed. Further, the samples must each be carefully labeled, and the worker must keep close track of his or her location when each sample is removed. Because of the arduous nature of this task, growers typically take only one sample in a field of interest, or at most a few samples across a field or area of interest and then average the results. The farmer will then apply fertilizers and other nutrients to the soil as if the soil's level of nutrients were uniform across the field, which is in fact not generally the case. The result is a poor approximation of the optimal nutrient level for each plot of soil, since some plots will likely be under fertilized and others will be over fertilized. Under fertilized plots will produce poor yields, and over fertilized plots may both produce poorer than optimum yields and also result in a waste of fertilizers. The wasted fertilizer not only is an added expense for the grower, but also exacerbates environmental issues that may arise from the later run-off of the excessive fertilizer due to rain or wind.
With the wide availability of global positioning system (GPS) satellite receivers today, the use of GPS information in soil sampling is rapidly increasing. GPS receivers have in fact become a staple of modern commercial farming equipment. The use of GPS in conjunction with manual soil sampling, however, only provides modest improvements in accuracy and efficiency. Although the grower now has precise information about where each sample is taken, manual sampling procedures still require a worker to travel to each identified point in the field of interest, remove a sample by hand, and then label and transport that sample for analysis. Thus it would be highly desirable to develop a soil sampling system that would periodically sample the soil across a field, while automatically keeping track of where samples were removed using GPS information, and automatically separating the samples according to location for ease of analysis. Such a system would ideally allow the operator to simply program the sampling mechanism for movement around the field or fields of interest in a regular pattern, while the mechanism performs sampling in a manner that is automatic and effectively transparent to the operator.
The related art includes several attempts to develop soil sampling mechanisms that periodically sample soil over an area. U.S. Pat. No. 3,224,512 to Alexander teaches a soil sampler that is mounted on a trailer and powered by a hydraulic system. The device is intended to be pulled by a tractor around a field, and the motion of one of the vehicle wheels activates a piston and cam-drive arrangement in communication with the soil sampler's hydraulics. Since the sampling periodicity is driven by the motion of one of the wheels on the trailer, the device automatically samples soil at regular intervals, regardless of the speed of the tractor pulling the trailer. The device uses a sampling tube that is forced into the ground for sample collection. Since the device does not stop in order for samples to be taken, the sampling tube is designed to pivot upon entry into the ground. The sampling tube is returned to its original insertion position (angled toward the front of the trailer) by means of a spring.
U.S. Pat. No. 3,625,296 to Mabry et al. teaches another soil sampling device that is mounted on a trailer, and which is intended to periodically sample soil over which the trailer passes. A digger foot is used to collect the soil sample, the foot being mounted at the end of a lever that includes a cam follower at its opposite end. By means of the cam follower, a cam on one of the tractor's wheels forces the digger foot into the ground as the trailer travels, thereby scooping a soil sample. As the cam rolls forward, the digger foot is released and a spring biases the digger foot upward, where it strikes a bumper block and deposits the soil sample into a collection container. Like the Alexander device, the Mabry et al. device automatically samples soil at regular intervals, since its sampling periodicity is driven by the distance traveled by the cam-equipped tractor wheel.
U.S. Pat. No. 5,741,983 to Skotnikov et al. teaches a third trailer-mounted automatic soil sampling device. In this case, an odometer is used to monitor the distance of travel of the trailer, which drives the sampling period of the device. The device utilizes a shaft-drive and linkage arrangement to control the period of the sampling action based upon the rotation of one of the trailer's wheels. A complex linkage arrangement allows the sampling tube to be raised into a position to eject and deposit a sample during each sampling cycle. The device further includes a bagging mechanism, whereby each of the samples that are drawn from the ground may be automatically bagged and labeled for later laboratory analysis.
The automatic sampling mechanisms described above suffer from important disadvantages that have limited their adoption in large commercial farming operations. Mechanisms that simply scoop a sample of material from the top of the ground are undesirable, since such a sample may not be representative of the lower levels of the soil in the area that is sampled. The most relevant section of the soil is that section that will be in greatest contact with the roots of the crop to be planted, which in the case of almost all commercial crops will be soil that lies at some distance below the surface. Further, in many applications the most desirable sample will be one that spans a section of the soil, from the surface to a pre-determined depth beneath the surface. A scooping mechanism will likely be unable to probe deeply enough to produce a sufficient sample to meet this need.
Although sampling mechanisms that insert a tube into the ground to collect a sample are superior to scoop mechanisms in many applications, the tube-type sampling mechanisms known in the art also suffer from important disadvantages. It is desirable in an automatic sampling mechanism that the sample be taken without requiring the vehicle that is carrying the sampling mechanism to stop. This greatly simplifies the task of the operator of the vehicle, since sampling can be automatically performed as the vehicle follows a pre-determined course over a field of interest, and also because it will save the operator a significant amount of time during the sampling process. The process of inserting and removing a tube from a moving vehicle, however, presents a number of difficulties. In one case these difficulties have been addressed by the use of a tube that pivots, thereby allowing the tube to be inserted into the ground at a forward-sloped angle, while it pivots rearwardly until the tube is removed. Depending upon the hardness of the soil, however, this may create a great deal of stress upon the tube. The pivoting action causes the tube to push backward against soil that is rearward of the tube at its distal end, and push forward against soil that is forward of the tube at its proximal end. While this may be a workable solution in very loose, highly compressible soil, this will likely lead to bending, excessive wear, or other damage to the tube in more firmly packed soil, such as many clay-based soils, or soil that may contain rocks or other hard obstacles.
Another solution to the problem of vehicle motion while the tube is inserted in the ground is a complex linkage arrangement that allows the structure immediately supporting the sampling tube to “follow” the tube during the portion of the sampling cycle when the tube is inserted into the ground. While this arrangement may avoid the problems presented by tube rotation, the structure and linkages necessary for this functionality are complex, and would likely be expensive to manufacture and difficult to maintain.
Regardless of how the tube is inserted in the ground, the prior art does not disclose a simple, efficient means to remove soil from the sampling tube once it is removed from the ground. Depending upon the composition and moisture content of the soil, the soil may be prone to stick within the tube. In addition, movement of the tube after the sample is withdrawn from the soil may cause compaction in the tube. The addition of a mechanical ejectors adds significant complexity to the sampling machine, and it would be desirable therefore to avoid the necessity of a mechanical ejector while maintaining consistent, smooth ejection across a variety of soil types and moisture levels.
Another disadvantage of the systems described above is that they do not take advantage of the efficiencies that may be achieved with the use of GPS information during sampling. Mapping of a field of interest, and selection of areas within the field for individual analysis, is greatly simplified using GPS information, and furthers the goal of making the process as transparent and automatic for the operator as possible.
What is desired then is an automatic soil sampling mechanism that facilitates the sampling of soil across an area of interest by simply tracing the mechanism over the area, while also being inexpensive to manufacture and simple to maintain, and taking advantage of GPS information. The limitations of the prior art are overcome by the present invention as described below.